A sliding rail assembly includes an upper sliding rail and a lower sliding rail extending along a back-and-forth direction as well as an upper ball and a lower ball disposed therebetween. The lower sliding rail includes a horizontal base plate, a first vertical side plate connected to the upper portion at the left edge of the horizontal base plate, and a first horizontal top plate connected to the right side at the upper edge of the first vertical side plate; the upper sliding rail comprises a first inclined plate and a second inclined plate; the extension line of the first inclined plate with the first vertical side plate and the extension line of the first horizontal top plate to form an upper triangular region; the extension line of the second inclined plate intersects the horizontal base plate and the first vertical side plate to form a lower triangular region.